Field
The present invention relates to a semiconductor device wherein a via hole is formed through the semiconductor substrate.
Background
In a case where electrical conduction is provided between a front surface of a substrate on which a semiconductor device is formed and a back surface opposite from the front surface, a via hole is provided in the semiconductor substrate to connect an electrode on the front surface side and a metal film on the back surface side through the via hole (see, for example, JP 10-303198 A).
When a semiconductor device of this conduction is manufactured, the electrode is first formed on the front surface of the semiconductor substrate. Subsequently, the semiconductor substrate is ground at the back surface side until the semiconductor substrate has a predetermined thickness. Subsequently, the back surface of the semiconductor substrate except the place for formation of the via hole is masked with a resist or the like and the semiconductor substrate is etched from the back surface side until the electrode is exposed. The mask is removed, the semiconductor substrate is cleaned, and the metal film is thereafter formed on the back surface, a side wall of the via hole and the lower surface of the electrode. Because the back surface of the electrode is exposed in the via hole, the electrode on the front surface side and the metal film on the back surface side contact each other.
With the increase in the degree of integration of semiconductor devices, the sizes of via holes in planar directions have been reduced. There is, therefore, a need to further improve the anisotropy of dry etching so that via holes are not expanded in horizontal directions when the via holes are formed. For this reason, a film formed on a via hole side wall in a semiconductor device at the time of etching is made stronger in order to avoid etching in lateral directions. A residue which cannot be completely removed by removal/cleaning after etching then remains on the via hole side wall. When the semiconductor device is heated after the via hole is formed, a pressure is applied to the interface between the semiconductor substrate and the metal film by a gas generated from a residue covered with the metal film on the back surface side. This pressure is transmitted through the interface to expand the interface between the electrode and the metal film having low adhesion strength. As a result, the connection between the electrode and the metal film is severed and the electrical conduction between the electrode and the metal film is lost.